Backpack



FIG. 1 is a front elevational view of a backpack showing my new design;

FIG. 2 is a left side elevational view thereof shown in the position of use, the right side being a miror image, and the broken lines showing a portion of the human figure being included to illustrate the use and not forming any part of the claimed design;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a top plan view thereof; and,

FIG. 5 is a bottom plan view thereof. 

I claim the ornamental design for a backpack, as shown and described. 